Josephson Frequency Singularity in the Noise of Normal Metal-Superconductor Junctions

TL;DR

This paper predicts a Josephson frequency singularity in the noise spectrum of normal metal-superconductor junctions below the gap, proposing the non-stationary Aharonov-Bohm effect as a detection method.

Contribution

It introduces a novel prediction of noise singularities at the Josephson frequency and suggests a new experimental approach using the non-stationary Aharonov-Bohm effect.

Findings

Singularity at Josephson frequency in noise spectral density predicted

Jumps in noise derivative occur at specific frequencies related to bias

Additional singularities predicted above the superconducting gap

Abstract

A singularity at the Josephson frequency in the noise spectral density of a disordered normal metal -- superconductor junction is predicted for bias voltages below the superconducting gap. The non-stationary Aharonov-Bohm effect, recently introduced for normal metals, is proposed as a tool for detecting this singularity. In the presence of a harmonic external field, the derivative of the noise with respect to the voltage bias reveals jumps when the applied frequency is commensurate with the Josephson frequency associated with this bias. The height of these jumps is non-monotonic in the amplitude of the periodic field. The superconducting flux quantum enters this dependence. Additional singularities in the frequency dependent noise are predicted above gap.